- Acute Flaccid Myelitis
- Alzheimer’s Disease
- Arteriovenous Malformations
- Attention Deficit Hyperactivity Disorder
- Back Pain
- Brain Aneurysm
- Brain Tumors
- Carpal Tunnel Syndrome
- Childhood Brain Tumors
- Delirium
- Dementia
- Hemorrhagic Stroke
- Ischemic Stroke
- Memory
- Meningitis
- Mild Cognitive Impairment
- Movement Disorders
- Multiple Sclerosis
- Neuroblastoma
- Neuromuscular Disorders
- Parkinson’s Disease
- Polio and Post-Polio Syndrome
- Speech and Language Problems in Children
- Stroke
- Transient Ischemic Attack
- Tremor
- Walking Problems
- West Nile Virus
- A1C
- Blood Glucose
- Diabetes
- Diabetes and Pregnancy
- Diabetes Complications
- Diabetes in Children and Teens
- Diabetes Medicines
- Diabetes Type 1
- Diabetes Type 2
- Diabetic Diet
- Diabetic Eye Problems
- Diabetic Foot
- Diabetic Heart Disease
- Diabetic Kidney Problems
- Diabetic Nerve Problems
- How to Prevent Diabetes
- Hyperglycemia
- Metabolic Syndrome
- Prediabetes
- Abortion
- Breast Cancer
- Breast Diseases
- Breast Reconstruction
- Breastfeeding
- Cervical Cancer
- Cervical Cancer Screening
- Cesarean Delivery
- Childbirth
- Ectopic Pregnancy
- Endometriosis
- Female Infertility
- Health Problems in Pregnancy
- High Blood Pressure in Pregnancy
- HIV and Pregnancy
- Hormone Replacement Therapy
- HPV
- Hysterectomy
- Infections and Pregnancy
- Mammography
- Mastectomy
- Menopause
- Menstruation
- Miscarriage
- Ovarian Cancer
- Ovarian Cysts
- Ovarian Disorders
- Pelvic Floor Disorders
- Pelvic Inflammatory Disease
- Pelvic Pain
- Period Pain
- Polycystic Ovary Syndrome
- Pregnancy
- Pregnancy and Drug Use
- Pregnancy and Opioids
- Premenstrual Syndrome
- Prenatal Care
- Prenatal Testing
- Primary Ovarian Insufficiency
- Sexual Problems in Women
- Stillbirth
- Teenage Pregnancy
- Trichomoniasis
- Tubal Ligation
- Uterine Cancer
- Uterine Diseases
- Uterine Fibroids
- Vaginal Bleeding
- Vaginal Cancer
- Vaginal Diseases
- Vaginitis
- Vulvar Cancer
- Vulvar Disorders
- Yeast Infections
- Alcohol
- Calcium
- Child Nutrition
- Cholesterol
- Cholesterol Levels: What You Need to Know
- Cholesterol Medicines
- DASH Eating Plan
- Eating Disorders
- Food Allergy
- HDL: The “Good” Cholesterol
- High Cholesterol in Children and Teens
- How to Lower Cholesterol
- How to Lower Cholesterol with Diet
- Infant and Newborn Nutrition
- LDL: The “Bad” Cholesterol
- Malabsorption Syndromes
- Nutrition for Older Adults
- Pregnancy and Nutrition
- Toddler Nutrition
- Triglycerides
- VLDL Cholesterol
- Alpha-1 Antitrypsin Deficiency
- Ataxia Telangiectasia
- Brain Malformations
- Cerebral Palsy
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- Cystic Fibrosis
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- Newborn Screening
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- Acute Lymphocytic Leukemia
- Allergy
- Animal Bites
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- Aplastic Anemia
- Asthma
- Asthma in Children
- Childhood Leukemia
- Childhood Vaccines
- Chronic Lymphocytic Leukemia
- COVID-19 Vaccines
- Cryptosporidiosis
- Eosinophilic Disorders
- Eosinophilic Esophagitis
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- HIV and Infections
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- Pemphigus
- Pneumocystis Infections
- Rheumatoid Arthritis
- Scleroderma
- Sjogren’s Syndrome
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- Vaccines
- Viral Infections
- Adhesions
- Ankle Injuries and Disorders
- Arm Injuries and Disorders
- Back Injuries
- Brachial Plexus Injuries
- Burns
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- Concussion
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- Dislocated Shoulder
- Dislocations
- Elbow Injuries and Disorders
- Eye Injuries
- Facial Injuries and Disorders
- Finger Injuries and Disorders
- Foot Injuries and Disorders
- Fractures
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- Heel Injuries and Disorders
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- Inhalation Injuries
- Insect Bites and Stings
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- Knee Injuries and Disorders
- Leg Injuries and Disorders
- Mosquito Bites
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- Rotator Cuff Injuries
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- Traumatic Brain Injury
- Wrist Injuries and Disorders
- Acute Bronchitis
- Bird Flu
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- Croup
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- Flu
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- Legionnaires’ Disease
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- Sleep Apnea
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- Anatomy
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- Birth Control
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- Male Infertility
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- Prostate Cancer
- Prostate Cancer Screening
- Prostate Diseases
- Reproductive Hazards
- Sexual Health
- Sexual Problems in Men
- Sexually Transmitted Diseases
- Syphilis
- Testicular Cancer
- Testicular Disorders
- Vasectomy
- Abdominal Pain
- Bad Breath
- Bleeding
- Breathing Problems
- Bruises
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- Chronic Pain
- Constipation
- Cough
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- Edema
- Fainting
- Fever
- Frostbite
- Gas
- Gastrointestinal Bleeding
- Headache
- Heartburn
- Heat Illness
- Hives
- Hypothermia
- Indigestion
- Itching
- Jaundice
- Nausea and Vomiting
- Pain
- Rare Diseases
- Raynaud’s Disease
- Sciatica
- Speech and Communication Disorders
- Stuttering
Vaccines
Summary
What are vaccines?
Vaccines are injections (shots), liquids, pills, or nasal sprays that you take to teach your body’s immune system to recognize and defend against harmful germs. For example, there are vaccines to protect against diseases caused by:
- Viruses, like the ones that cause the flu and COVID-19
- Bacteria, including tetanus, diphtheria, and pertussis
What are the types of vaccines?
There are several types of vaccines:
- Live-attenuated vaccines use a weakened form of the germ.
- Inactivated vaccines use a killed version of the germ.
- Subunit, recombinant, polysaccharide, and conjugate vaccines use only specific pieces of the germ, such as its protein, sugar, or casing.
- Toxoid vaccines that use a toxin (harmful product) made by the germ.
- mRNA vaccines use messenger RNA, which gives your cells instructions for how to make a protein (or piece of a protein) of the germ.
- Viral vector vaccines use genetic material, which gives your cells instructions for making a protein of the germ. These vaccines also contain a different, harmless virus that helps get the genetic material into your cells.
Vaccines work in different ways, but they all spark an immune response. The immune response is the way your body defends itself against substances it sees as foreign or harmful. These substances include germs that can cause disease.
What happens in an immune response?
There are different steps in the immune response:
- When a germ invades, your body sees it as foreign.
- Your immune system helps your body fight off the germ.
- Your immune system also remembers the germ. It will attack the germ if it ever invades again. This “memory” protects you against the disease that the germ causes. This type of protection is called immunity.
What are immunization and vaccination?
Immunization is the process of becoming protected against a disease. But it can also mean the same thing as vaccination, which is getting a vaccine to become protected against a disease.
Why are vaccines important?
Vaccines are important because they protect you against many diseases. These diseases can be very serious. So getting immunity from a vaccine is safer than getting immunity by being sick with the disease. And for a few vaccines, getting vaccinated can actually give you a better immune response than getting the disease would.
But vaccines don’t just protect you. They also protect the people around you through community immunity.
What is community immunity?
Community immunity, or herd immunity, is the idea that vaccines can help keep communities healthy.
Normally, germs can travel quickly through a community and make a lot of people sick. If enough people get sick, it can lead to an outbreak. But when enough people are vaccinated against a certain disease, it’s harder for that disease to spread to others. This type of protection means that the entire community is less likely to get the disease.
Community immunity is especially important for people who can’t get certain vaccines. For example, they may not be able to get a vaccine because they have weakened immune systems. Others may be allergic to certain vaccine ingredients. And newborn babies are too young to get some vaccines. Community immunity can help to protect them all.
Are vaccines safe?
Vaccines are safe. They must go through extensive safety testing and evaluation before they are approved in the United States.
What is a vaccine schedule?
A vaccine, or immunization, schedule lists which vaccines are recommended for different groups of people. It includes who should get the vaccines, how many doses they need, and when they should get them. In the United States, the Centers for Disease Control and Prevention (CDC) publishes the vaccine schedule.
It’s important for both children and adults to get their vaccines according to the schedule. Following the schedule allows them to get protection from the diseases at exactly the right time.
Start Here
- Adult Immunization Schedule: Recommendations for Ages 19 Years or Older, United States, 2023 Centers for Disease Control and Prevention
- Get Vaccines to Protect Your Health (Adults Ages 19 to 49) Office of Disease Prevention and Health Promotion
- Understanding How Vaccines Work Centers for Disease Control and Prevention
- Vaccine Basics Department of Health and Human Services
- Vaccines for Adults Mayo Foundation for Medical Education and Research
Health Check Tools
- Adult Vaccine Assessment Tool Centers for Disease Control and Prevention
Encyclopedia
- Antibody titer blood test Medical Encyclopedia
- Vaccines Medical Encyclopedia
- Vaccines – immunizations Medical Encyclopedia
Find an Expert
- Centers for Disease Control and Prevention Centers for Disease Control and Prevention
- National Institute of Allergy and Infectious Diseases National Institute of Allergy and Infectious Diseases
- National Vaccine Program Department of Health and Human Services, Office of Infectious Disease and HIV/AIDS Policy
Children
- Childhood Immunization: MedlinePlus Health Topic National Library of Medicine
Clinical Trials
- ClinicalTrials.gov: Vaccines National Institutes of Health
Specifics
- Current Vaccine Shortages and Delays Centers for Disease Control and Prevention
- There Are Vaccines You Need as an Adult Centers for Disease Control and Prevention
- Travelers’ Health: Destinations Centers for Disease Control and Prevention
- Vaccines.gov Department of Health and Human Services
- What Vaccines Are Recommended for You Centers for Disease Control and Prevention
- Who Should Not Get Vaccinated with These Vaccines? Centers for Disease Control and Prevention
Reference Desk
- Glossary of Vaccine Terms Centers for Disease Control and Prevention
- Overview of the Immune System National Institute of Allergy and Infectious Diseases
Patient Handouts
- Immunizations for people with diabetes Medical Encyclopedia
Related Issues
- Keeping Your Vaccine Records up to Date Centers for Disease Control and Prevention
- Vaccinations and Flu Shots for People with Cancer American Cancer Society
- Vaccinations for Adults with Diabetes Immunization Action Coalition
- Vaccine Safety: MedlinePlus Health Topic National Library of Medicine
- Vaccines Protect Your Community Department of Health and Human Services
- What’s in Vaccines? Centers for Disease Control and Prevention
Journal Articles
Statistics and Research
- Research: Vaccines National Institute of Allergy and Infectious Diseases
- Safeguarding Our Health: Vaccines Protect Us All National Institutes of Health
- VaxView: Vaccination Coverage in the U.S. Centers for Disease Control and Prevention
Diagnosis and Tests
- Screening Checklist for Contraindications to Vaccines for Adults Immunization Action Coalition
Women
- Summary of Maternal Immunization Recommendations Centers for Disease Control and Prevention
- Vaccines and Pregnancy Organization of Teratology Information Specialists
- Vaccines and Pregnancy: 8 Things You Need to Know Centers for Disease Control and Prevention
Older Adults
- Vaccinations and Older Adults National Institute on Aging
Images
- Vaccine-Preventable Disease Photos Immunization Action Coalition